A computer network, such as the Internet, allows end users using client computers to access information stored within, or associated with, server computers in the network. In general, content sources (e.g., server devices) on the network transmit requested information as content in the form of a file (e.g., text, audio, or video) or as a stream (e.g., a stored stream or a live stream) involving one-way, point-to-point delivery of a relatively large number of bits to the end users (e.g., client devices). Typically, the content sources transmit the files or streams to the end user or destination using a variety of distribution mechanisms.
One conventional distribution mechanism for content transmission involves one-to-one or point-to-point (e.g., unicast) transmission. In one-to-one transmission, a single content source, such as a server, transmits content to a single receiver, such as a client. In general, one-to-one transmission is an effective transmission mechanism on a small scale because the associated transmission and reception tools, such as client devices, and software have relatively low associated costs. One-to-one transmission is also an effective transmission mechanism because the network connection costs are relatively low.
Certain types of network applications, such as conventional presence systems, provide a client device with content (e.g., presence information) relating to the availability of other users on the network (e.g., whether “online” or “offline”) using one-to-one (e.g., unicast) transmission. A conventional presence system, for example, allows users to subscribe to each other (e.g. place each other on a contact list or a buddy list) and receive notification or presence information relating to the availability (e.g., “online” or “offline” status) of the subscribed users within the presence system. Based on receiving notification of a first user's online status, a second user can then decide whether and/or how (e.g., using instant messaging) to make contact with the first user.
A conventional presence system includes a number of users (e.g., content subscribers) in communication with a central site or presence server. When a first user (e.g., content subscriber) wants to receive the presence information associated with a second user, the first user transmits to the presence server a request (e.g., subscription request) for presence information related to the second user. In response, the presence server transmits presence information relating to the presence of the second user on the presence system. Each time that the presence information of the second user changes (e.g., the status of the second user changes from “online” to “offline”) the presence system, using the one-to-one transmission mechanism, delivers the changed presence information (e.g., a notification message) to the first user to indicate the change in availability or status of the second user.